Conventionally, waste plastics discarded from households and so on are disposed of by such means as incineration and burying. However, incineration and burying have been increasingly accompanied by an environmental impact, shortages of landfill areas, and other social problems. In recent years, work has progressed concerning the sorting/recovering and recycling of waste plastics, and for these reasons, identifying the types of waste plastics has been seen as extremely important. Also, in order to achieve processing for as much waste plastics as possible, there is a need for such identification to be performed with good accuracy and continuously.
Conventionally, methods of identifying types of waste plastics include methods that involve comparison of specific gravities, and methods using fluorescent X-rays or near-infrared light. However, it has been very difficult up until now to identify plastic types with good accuracy and continuously. For example, when there are almost no differences between the specific gravities of plastics, it is very difficult to use methods that involve weight comparisons. And for identification methods using near-infrared light, it is difficult to identify plastics when, for example, they are dark-colored plastics. However, for household electrical appliances discarded from households, for example, television receivers, there are many dark-colored waste plastics, and there are additional difficulties in identifying these with good accuracy because of such factors as surface coatings on the plastics, surface degradation due to long use, smearing of grime and other dirt, and the flame retardants contained within these products. It should be noted that throughout this specification, near-infrared light refers to the light whose wave number is in the range approximately from 4,000 cm−1 to 13,000 cm−1.
Furthermore, conventionally, identification is performed directly for household electrical appliances such as, for example, television receiver chassis. However, in recent years, the size of television receivers has been increasing, and the sizes of the discarded chassis also have been increasing. In terms of the tasks and labor required, it is difficult to directly identify these types of large-sized plastic products. Also, they make it difficult to introduce continuous lines at recycling plants and inevitably involve increasing the size of the equipment required for identification.